1. Technical Field
This invention relates to equol and its use as a therapeutic compound for treating and preventing physiological and pathophysiological conditions mediated by androgens. Specifically, the present invention relates to the use of equol for preventing or treating neuropsychiatric or neurodegenerative diseases or disorders.
2. Background Information
In recent years phytoestrogens have received increased investigative attention due to their potential protective effects against age-related diseases (e.g. cardiovascular disease and osteoporosis) and hormone-dependent cancers (i.e., breast and prostate cancer). There are three main classifications of phytoestrogens: 1) isoflavones (derived principally from soybeans), 2) lignans (found in flaxseed in large quantities) and 3) coumestans (derived from sprouting plants like alfalfa). Of these three main classifications, human consumption of isoflavones has the largest impact due to its availability and variety in food products containing soy. Of the isoflavones, genistein and daidzein are thought to exert the most potent estrogenic hormone activity and thus most attention has been directed toward these molecules (Knight D. C. et al., Obstet Gyneco, 187:897-904, (1996); Setchell, K. D. R. Am J Clin Nutr, 129:1333S-1346S (1998); Kurzer, M. S. et al., Annu Rev Nutr, 17:353-381(1997)). However, these isoflavone molecules do not exist at high levels in their biologically active form in soy foods, but rather are at high abundance in a precursor form. For example, genistin, the precursor of genistein, is the glycosidic form that contains a carbohydrate portion of the molecule. Additionally, malonylglucoside and acetylglucoside forms also are found. These conjugates are metabolized in the GI tract by intestinal bacteria, which hydrolyze the carbohydrate moiety to the biologically active phytoestrogen, genistein. The same metabolic step occurs for the aglycone daidzein, which is converted from the glycosidic form daidzein. Daidzein is then further metabolized to equol in an “equol-producing” mammal. Thereafter, equol circulates in the blood stream at very high concentrations. Equol is not normally present in the urine of most healthy adults unless soy is consumed. The formation of equol in vivo is exclusively dependent on intestinal microflora as evidenced from the finding that germ-Phyto-Free animals do not excrete equol, and that equol is not found in the plasma and urine of newborn or 4-month old infants fed exclusively soy foods from birth due to the fat that the intestinal flora has not yet developed in neonates. See Setchell K. D. R. et al., The Lancet 1997; 350:23-27.
The phenolic ring structures of isoflavones enable these compounds to bind estrogen receptors (ER) and mimnic estrogen. Although genistein and daidzein bind to ER, it is with a lower affinity when compared to estradiol, and with a greater affinity for ERβ than to ERα. Additionally, phytoestrogens have been reported to act like natural selective estrogen receptor modulators (SERMs) at various tissue sites throughout the body. In some tissues, there is evidence that phytoestrogens act as estrogen agonists, whereas in others, they display antagonistic characteristics comparable to that of tamoxifen or raloxifene where SERM activity appears to be sex-hormone and gender dependent.
While the bulk of the scientific literature has focused on the natural isoflavones in soy or clover, little has been reported on the actions or effects of their intestinally derived metabolites.
Equol (7-hydroxy-3(4′hydroxyphenyl)-chroman) represents the major metabolite of the phytoestrogen daidzein, one of the main isoflavones found abundantly in soybeans and soy-foods. Equol, however, is not a phytoestrogen, because it is not a natural constituent of plants. Equol does not occur naturally in any plant-based products. Rather, it is a non-steroidal isoflavone that is exclusively a product of intestinal bacterial metabolism (relatively few individuals, ˜30-400%, have the micro flora necessary to convert soy isoflavones to equol). Previous research with equol has identified that equol possess some weak estrogenic properties, binds sex hormone binding globulin, binds α-fetoprotein, and has anti-oxidant activity. However, equol is unique among the plant-derived isoflavones in that it possesses a chiral center and as such exists as two distinct enantiomeric forms, the R- and S-enantiomers. We have shown that the S-enantiomer of equol is the exclusive equol form found in the urine and plasma of “equol-producing” mammals consuming soy, and is the only equol enantiomer made by human intestinal bacteria. All previous studies on equol appear to have been conducted with the racemic form of equol. There has in general been a lack of appreciation that two forms of equol exist and to our knowledge no previous study has reported on the specific actions or activity of the individual enantiomers. The R- and S-enantiomers conformationally differ, which subsequently influences their biological activity. For example, only the S-enantiomer of equol binds estrogen receptor (ER) with sufficient affinity to make it relevant to bind circulating equol levels reported in humans. Compared to 17β-estradiol the relative binding affinities of the R- and S-equol enantiomer for ERα are 210.6 and 49.2 fold less respectively. However, the S-equol enantiomer seems to be largely ERβ-selective with a relatively high affinity for ERβ. Enantiomer S-equol binds ERβ at approximately 20% that of 17β-estradiol [equol, Kd=0.7 nM vs. 17β-estradiol, Kd=0.15 nM], while the R-equol enantiomer binds at approximately 100 fold less. R-Equol, although not naturally occurring, is of considerable importance because of its ability to modulate androgen-mediated processes in the body.
The prostate gland depends on androgen hormone action for its development and growth, and the development of human benign prostatic hyperplasia (BPH) clearly requires a combination of testicular androgens during the aging process. However, testosterone is not the major androgen responsible for growth of the prostate. The principal prostatic androgen is 5α-dihydrotestosterone (5α-DHT), as evidenced by current treatments of prostatic cancer are directed toward reducing 5α-DHT with 5α-reductase inhibitors. Although not elevated in human BPH, 5α-DHT levels in the prostate remain at a normal level with aging, despite a decrease in the plasma testosterone. Testosterone is converted to 5α-DHT by 5α-reductase in prostatic stromal and basal cells. 5α-DHT is primarily responsible for prostate development and the pathogenesis of BPH. Inhibitors of 5α-reductase reduce prostate size by 20% to 30%. This reduction in glandular tissue is achieved by the induction of apoptosis, which is histologically manifested by ductal atro-phy. 5α-reductase occurs as 2 isoforms, type 1 and type 2, with the prostate ex-pressing predominantly the type-2 isoform, and the liver and skin expressing primarily the type-1 isoform. Patients have been identified with deficiencies in the type-2 5α-reductase, but not type 1. Knockout mice with the type-2 5α-reductase null-mutation demonstrate a phenotype similar to that seen in men with 5α-reductase deficiency. Type-1 5α-reductase knockout male mice are phenotypically normal with respect to reproductive function. Enzymatic activity for 5α-reductase or immunohistochemical detection has been noted in other genitourinary tissues, such as the epididymis, testes, gubemaculum, and corporal cavemosal tissue.
Quantitatively, women secrete greater amounts of androgen than of estrogen. The major circulating steroids generally classified as androgens include dehydroepiandrosterone sulphate (DHEAS), dehydroepiandrosterone (DHEA), androstenedione (A), testosterone (T), and 5α-DHT in descending order of serum concentration, though only the latter two bind the androgen receptor to a significant degree. The other three steroids are better considered as pro-androgens. 5α-DHT is primarily a peripheral product of testosterone metabolism. Testosterone circulates both in its free form, and bound to protein including albumin and sex steroid hormone-binding globulin (SHBG), the levels of which are an important determinant of free testosterone concentration. The postmenopausal ovary is an androgen-secreting organ and the levels of testosterone are not directly influenced by the menopausal transition or the occurrence of menopause.
The work of some research has focused on the development of steroidal compounds for the treatment of androgen dependent diseases such as: hirsutism, androgenic alopecia, benign prostatic hyperplasia (BPH) and prostate cancer. 5α-DHT has been implicated as a causative factor in the progression of these diseases, largely through the clinical evaluation of males who are genetically deficient of steroid 5α-reductase enzyme. As a result of such studies, the inhibition of this enzyme has become a pharmacological strategy for the design and synthesis of new antiandrogenic drugs. However, it is unclear whether inhibition of 5α-reductase will have a deleterious impact on the system, as evidenced by contraindications arising from reported side effects of conventional treatments using 5α-reducatse inhibitors. The development of different strategies that target the inhibition of 5α-DHT effects would be a major advance in the therapy of androgen-mediated conditions.